Conventional network devices suffer from a problem that they cannot be externally controlled to achieve flexible control, such as load balancing and biasing. Accordingly, an increase in the network size makes it difficult to monitor and improve the behavior of the system, requiring a huge cost for changing the design and configuration.
As a technique for solving such a problem, an approach has been proposed in which the packet transfer function and the route control function of network devices are separated. If network devices are responsible for the packet transfer function and a controller externally provided separately from the network devices are responsible for the control function, for example, this allows the controller to perform centralized management of packet transfers, enabling establishment of a flexible network.